A. Zocchi, G. Bertin, A. L. Varri
We perform a systematic combined photometric and kinematic analysis of a
sample of globular clusters under different relaxation conditions, based on
their core relaxation time (as listed in available catalogs), by means of two
well-known families of spherical stellar dynamical models. Systems
characterized by shorter relaxation time scales are expected to be better
described by isotropic King models, while less relaxed systems might be
interpreted by means of non-truncated, radially-biased anisotropic f^(\nu)
models, originally designed to represent stellar systems produced by a violent
relaxation formation process and applied here for the first time to the study
of globular clusters. The comparison between dynamical models and observations
is performed by fitting simultaneously surface brightness and velocity
dispersion profiles. For each globular cluster, the best-fit model in each
family is identified, along with a full error analysis on the relevant
parameters. Detailed structural properties and mass-to-light ratios are also
explicitly derived. We find that King models usually offer a good
representation of the observed photometric profiles, but often lead to less
satisfactory fits to the kinematic profiles, independently of the relaxation
condition of the systems. For some less relaxed clusters, f^(\nu) models
provide a good description of both observed profiles. Some derived structural
characteristics, such as the total mass or the half-mass radius, turn out to be
significantly model-dependent. The analysis confirms that, to answer some
important dynamical questions that bear on the formation and evolution of
globular clusters, it would be highly desirable to acquire larger numbers of
accurate kinematic data-points, well distributed over the cluster field.
View original:
http://arxiv.org/abs/1201.1466
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